FIG. 7 is a schematic cross sectional diagram showing the configuration of a semiconductor device in which a conventional MPU is mounted.
As shown in FIG. 7, a nickel plating layer 2 is formed on the outer surface of a base 1 made of, for example, a copper-tungsten alloy having high thermal conductivity. A semiconductor chip 5, which is a semiconductor element, is bonded and secured to the surface of the plating layer 2 with a conductive resin layer 4 including a metal and having high thermal conductivity in between. A ceramic package 6 is placed in such a manner as to cover the semiconductor chip 5 and is bonded and secured to the surface of the plating layer 2 with the conductive resin layer 4 in between. Conventional semiconductor devices are formed in this manner.
A substrate for a semiconductor device where an thin film of an insulator of, for example, Al2O3 or diamond, is formed on a metal plate is proposed as a substrate for a semiconductor device having excellent heat releasing properties where the coefficient of thermal expansion is close to that of the semiconductor element to be mounted in Japanese Unexamined Patent Publication S58 (1983)-15241 (Patent Document 1).
In addition, a substrate on which a semiconductor element is to be mounted where an electrically insulating layer is formed of diamond, a carbon film in pseudo diamond form or a mixed substance of these on a metal substrate is proposed as a substrate on which a semiconductor element is to be mounted having low thermal resistance and only little influence on a high frequency signal in Japanese Unexamined Patent Publication S60 (1985)-128625 (Patent Document 2).
Furthermore, a substrate on which a semiconductor element is to be mounted made of a main metal plate made of a copper-tungsten alloy or a copper-molybdenum alloy and a tungsten plate or a molybdenum plate which is bonded to this plate and has an electrically insulating coating layer of, for example, Al2O3 or diamond, on at least a portion of the surface is proposed in Japanese Unexamined Patent Publication S61 (1986)-194842 (Patent Document 3) in order to solve the problems caused by pinholes and cracking which occur in the electrically insulating coating layer.
A substrate for a semiconductor device having a base made of a tungsten and/or molybdenum-copper alloy, an aluminum coating layer that is formed on the surface of the base to which a resin is to be joined, and an oxide layer having a thickness of 10 angstrom to 800 angstrom created through natural oxidation on the surface of the aluminum coating layer is proposed in Japanese Unexamined Patent Publication H10 (1998)-284643 (Patent Document 4) in order to improve the strength of joining between the substrate material made of an alloy such as copper-tungsten or copper-molybdenum and a resin.    Patent Document 1: Japanese Unexamined Patent Publication S58 (1983)-15241    Patent Document 2: Japanese Unexamined Patent Publication S60 (1985)-128625    Patent Document 3: Japanese Unexamined Patent Publication S61 (1986)-194842    Patent Document 4: Japanese Unexamined Patent Publication H10 (1998)-284643